1. Field of the Invention
The present invention relates to a brightness calculating apparatus, a control method for the brightness calculating apparatus, and a display apparatus.
2. Description of the Related Art
Conventionally, there is a technique for controlling emission brightness of a backlight and transmittance of a liquid crystal panel based on an image signal for each divided region that is obtained by dividing a screen of a liquid crystal display apparatus (refer to Japanese Patent Application Laid-open No. 2002-99250). Using such a technique enables an unacceptably bright black level of a dark part of an image to be suppressed and contrast to be enhanced.
Generally, brightness on an emission surface (a surface that emits light) of a backlight is not uniform. Controlling the transmittance of a liquid crystal panel in accordance with emission brightness of a backlight without taking brightness distribution on an emission surface into consideration prevents an accurate gradation expression from being performed (causes an error in a gradation expression) and diminishes the contrast enhancement effect described above. Therefore, in order to obtain a high contrast enhancement effect, the brightness distribution on the emission surface (the brightness of each position on the emission surface) must be accurately estimated and the transmittance of the liquid crystal panel must be controlled (an image signal must be corrected) in consideration of an estimation result. An example of a technique for estimating a brightness distribution on an emission surface and correcting an image signal based on an estimation result thereof is disclosed in Japanese Patent Application Laid-open No. 2010-164851.
A backlight (surface light source) capable of controlling emission brightness for each divided region has a plurality of sub surface light sources corresponding to a plurality of divided regions. The plurality of sub surface light sources can be individually controlled. For example, the sub surface light sources have a direct backlight structure (a structure in which a light source such as an LED is arranged directly underneath a screen and light from the light source is diffused by a diffuser plate). In the case of such a backlight, the brightness at each position on the emission surface of the backlight is affected not only by light from a corresponding sub surface light source but also by light from other sub surface light sources. Therefore, in order to accurately calculate the brightness at each position on the emission surface, the light from other sub surface light sources must be taken into consideration in addition to the light from a corresponding sub surface.
Conceivable methods of accurately calculating the brightness at each position on an emission surface include a method in which, for each position on the emission surface, brightness of light from each sub surface light source at the position is calculated, and for each position on the emission surface, a total value of the brightness of the position (the brightness of each sub surface light source) is calculated.
However, such methods involve an enormous amount of computations for calculating the brightness at each position on an emission surface. In particular, an enormous amount of computations is required when there are a large number of sub surface light sources.